Solvent extraction method

Abstract

A method for solvent extracting extractable materials from solids is disclosed, which includes (a) maintaining a vertically extending bed comprising said solids in a vertically extending extraction zone and introducing said mixture into an upper portion of said bed; (b) providing a substantially continuous gaseous phase in contact with a lower portion of said bed; (c) maintaining a substantially continuous liquid phase comprising a vaporizable primary liquid solvent and at least one secondary liquid solvent in contact with at least a lower part of said upper portion of said bed above said gaseous phase, said liquid phase and said gaseous phase having an interface at a vertically intermediate level of said bed; (d) introducing said primary liquid solvent into an intermediate liquid level in said liquid phase spaced from the top of said liquid phase; (e) introducing at least one secondary liquid solvent into said liquid phase above said intermediate liquid level; (f) passing said primary and secondary solvents through said liquid phase, extracting said extractable component from said mixture into said liquid phase, and removing said extractable component and said solvents from said extraction zone; (g) preventing said liquid phase from flowing downwardly through said lower portion of said bed by maintaining said gaseous phase at a pressure sufficient to support said liquid phase thereon and vaporizing said primary solvent adhering to solids in said lower portion of said bed; and (h) removing solids from said lower portion of said bed.